The present invention relates to a multicavity klystron.
Klystrons of the type described have been improved in efficiency from 30%-40% to about 50%. Efforts to increase the efficiency up to 60%, however, often have met with unstable operational conditions such as ringing on heavy pulse signals and oscillation. A source of such unstable operational phenomena has been considered to be secondary electrons back-streaming in a direction reverse to that of the primary electrons emitted from the electron gun toward the collector.
As a prior attempt to reduce such back-streaming secondary electrons, U.S. Pat. No. 3,940,655 discloses that the central axis in the high-frequency circuit region is displaced from the central axis in the collector region, thereby causing the high-energy secondary electrons which travel at substantially the same speed as that of the primary electrons, to make asymmetrical collision so that the number of secondary electrons back-streaming into the high-frequency circuit region can be reduced. According to U.S. Pat. No. 3,936,695, a plurality of conductive baffle members extend inwardly from the internal surface of the collector to limit the path in which the high-energy secondary electrons can travel back into the high-frequency circuit region.
The prior art proposals have been based on the assumption that the back-streaming electrons are constituted by secondary electrons generated by bombardment of the primary beam of electrons upon a surface in the collector region. According to the afore-mentioned U.S. patents, however, the tubes are complicated in structure, and no effective means can be provided for eliminating unstable operational phenomena in high-efficiency klystrons.